Comparators are well known in prior art and have been developed to a high degree. Typically, such devices compare one analog voltage to another and provide a digital output that indicates which input voltage is higher than the other. Ordinarily, the comparator is simply a high gain direct coupled amplifier with a differential input stage. Linear integrated circuit technology is typically used to fabricate high quality precision comparators. Generally, such devices must be trimmed during (or after) fabrication to achieve a suitably low offset voltage.
Using metal oxide semiconductor (MOS) technology it has proven very difficult to fabricate high gain linear amplifiers suitable for comparators. Accordingly, in D/A and A/D applications hybrid technology has been employed for high performance precision devices. More recently it has been found that suitable precision could be attained in MOS comparators if chopper stabilized capacitor coupled amplifier stages are employed. Thus, the comparator function could be integrated into a single chip using large scale integration (LSI) of MOS devices. Once the problem of switching transient suppression and metallization error compensation was solved, MOS comparators became practical. For example see the copending application of Thomas P. Redfern, Ser. No. 731,269, filed Oct. 12, 1976, now U.S. Pat. No. 4,075,509, and titled CMOS COMPARATOR CIRCUIT AND METHOD OF MANUFACTURE.